The present invention relates to a method of and apparatus for the laser treatment of occluded body lumens of mammals, especially humans, and more particularly to the intraluminal use of laser energy to perforate and/or remove luminal occlusions, such as thrombi and/or atherosclerotic plaques in the cardiovascular system.
Cardiovascular disease is a major cause of death and morbidity and manifests a grave concern to both the scientific community and the lay public. Arteriosclerotic cardiovascular pathophysiology is a complex of diseases which affects many blood vessels in the body, the decreased lumen diameter causing tissue ischemia. Other very common diseases, such as diabetes mellitus, enhance the occlusion of important blood vessels and ischemia of the organs they supply. These diseases, aggravated by such other common abnormalities as hypertension, and other vascular diseases and cardiovascular diseases, account for cerebrovascular accidents, myocardial infarctions, and other devastating illnesses, including loss of life and limb. Unfortunate individuals affected with arteriosclerotic cardiovascular disease and the related vasculopathies often manifest disease in coronary, carotid and cerebral arteries, in popliteal, tibial and dorsalis pedis arteries of the lower extremities and in other vessels. Those individuals, apart from having a shortened life expectancy, and suffering from sudden death frequently also suffer from debilitating problems including angina, shortness of breath and restricted activity, claudication or restricted use of the lower extremities, sometimes with loss of those extremities from disease, and loss of functions of movement, speech, cerebral interpretation and cognitive abilities.
Historically, there are few effective means for preventing some of these disastrous medical problems. Patients with certain types of coronary insufficiencies documented by certain coronary angiographic findings may be helped symptomatically by coronary artery bypass operations. Other patients sometimes may be benefited by other types of arterial surgery, for example, various bypass operations, or endarterectomies, which surgically attempt recanalization of certain occluded blood vessels or other operations. Those are generally patients with severe disease, but yet who meet certain diagnostic criteria and who are healthy enough to undergo what amounts to major surgery with relatively high morbidity and mortality rates. The cost is immense for many of these operations and incumbent hospitalization, including expensive special equipment which is required, and special training which is necessary for a team to operate this type of surgical equipment. For example, it is estimated that a single coronary bypass operation may cost a patient over $50,000 including the hospitalization fees, and surgical fees. Availability of this special type of surgery for vascular problems is limited. Long term efficacy of this type of surgery is as yet unknown, and the appropriate diagnostic and surgical criteria remain controversial. Because of the severity of the morphology and nature of the disease, for many patients treatment has been unavailable and has been beyond the current scope of surgical intervention. For example, many patients lose extremities or their lives by virtue of having these inoperable conditions.
In a different context, problems of lumens of the body, particularly small lumens, are complicated by occlusive diseases of other types. As an example in the nervous system, the Aqueduct of Sylvius, in the ventricular system of the brain, may be blocked in a child born with congenital hydrocephalus. This condition necessitates complicated and often unsuccessful corrective neurosurgical procedure known as shunting. Considering the genito-urinary system, for example, fallopian tubes may become occluded by inflammatory or other disease processes. This may cause infertility and is a common problem. There is no effective treatment for this problem at this point in time, and this has stimulated interest in a "test tube baby" controversy.
One suggested solution to the problem of atherosclerotic obstructions is a non-operative technique to improve coronary blood flow is known as percutaneous transluminal coronary angioplasty (PTCA). Generally, PTCA involves introducing a balloon catheter into the femoral artery or by brachial cutdown and fluoroscopic positioning at the appropriate coronary ostium. Pressure monitoring is also used to aid in positioning the balloon tip of the catheter at the stenosis. The balloon is inflated for 3-5 seconds to mechanically enlarge the stenosis and is then deflated for measurement of distal coronary pressure. The cycle may be repeated several times until a satisfactory decrease in pressure gradient is achieved.
Although the PTCA technique is sometimes effective to improve coronary blood flow, there are complications which must be weighed before undertaking the procedure. Such complications which may occur include arterial spasms, myocardial infarction, thrombotic occlusion, embolization and dissection, or frank perforation of the vessel wall.
It has also been suggested that cardiovascular occlusions, as well as occlusions in other body lumens, might be vaporized by means of laser energy. U.S. Pat. No. 4,207,874 to Choy, for example, discloses a flexible conduit which accommodates a fiberoptic bundle divided into light source, viewing and laser bundle portions. The flexible conduit is introduced into a vein or other body lumen and advanced until it contacts an obstruction such as a thrombus. A laser apparatus optically associated with the laser fiber bundle is then activated so that the laser energy vaporizes the obstruction, the remaining particles of which are then removed by suction.
Other flexible laser endoscopes for use in the therapeutic laser treatment of body lumens are disclosed in U.S. Pat. Nos. 4,072,147; 4,146,019; 4,170,997; and German Offenlegungsschrift No. 2,640,406. Such intraluminal laser devices typically are said to function by thermal vaporization and/or coagulation of the luminal obstruction mass.
One of the most serious risks inherent in the intraluminal use of laser radiation, especially in coronary or cerebral blood vessels, is the possibility of perforation of or thermal damage to the vessel walls and surrounding tissue. Accordingly, intravascular recanalization of occluded blood vessels is still an experimental procedure.
Recently, investigators have reported the use of continuous wave argon, neodymium-YAG and carbon dioxide laser sources to successfully vaporize, coagulate and penetrate atherosclerotic plaque in animals and in sections of coronary arteries taken from human cadavers. However, the investigators also report perforation of the vessel walls in many cases, particularly at laser energy levels which have been increased to a level sufficient to effect vaporization of the plaque.
Such laser energy levels are appropriately characterized as the "thermal" mode of laser operation which involves causing damage to tissue by virtue of heat accumulation in the tissue impinged by the laser radiation. Excessive heat accumulation causes thermal degradation or thermal necrosis. In other words, the temperature of the tissue rises, tissue proteins are denatured and ultimately the tissue is coagulated and "evaporated" or "vaporized." While the laser thermal energy mode is effective in coagulating and vaporizing many tissues, including the tissues forming atherosclerotic plaques and stenoses, its use heretofore in occluded coronary and cerebral blood vessels, for example, is not sufficiently safe and controllable. Consequently, the problem of inadvertent damage to or destruction of surrounding vessel tissue has been a major obstacle in the development of an acceptable microsurgical technique for laser angioplasty in the human vascular system.
Apart from the risk of using continuous wave laser energy in the human vascular system, the prior art intraluminal laser devices lack effective mechanisms for "aiming" the laser beam to minimize the possibility of inadvertent damage to the vessel walls and to maximize the exposure of a large area of the occlusion, e.g., the atherosclerotic plaque, to the laser energy.